Method of separating aromatic hydrocarbons from petroleum fractions



United States Patent Cfiice 3,291,851? Patented Dec. 13, 1966 3,291,851 METHOD OF SEPARATING AROMATIC HYDRO- CARBONS FROM PETROLEUM FRACTIQNS Ivor W. Mills, Glenolden, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Filed Oct. 4, 1962, Ser- No. 228,249 12 Claims. (Cl. 260-674) The present invention relates to a method of separating aromatic hydrocarbons from petroleum. More particularly it relates to a method of separating naphthalenic compounds from petroleum fractions. Specifically it relates to a method of obtaining alkylnaphthalenes from cracked gas oil containing alkylnaphthalenes in admixture with other aromatic and/or non aromatic hydrocarbons using an alkali metal complexing technique.

It is known that naphthalenic compounds, for example, polycyclic aromatic compounds such as the alkylnaphthalenes, are present in certain fractions derived from petroleum. Specifically, petroleum fractions which boil within the range of 375 to 600 F. generally contain substantial amounts of alkylnaphthalenes, such as mono-, di-, and tri-methylnaphthalenes and in smaller quantity, the ethylnaphthalenes. Recycle fractions, which are for-med in the cracking of petroleum stocks and which include this boiling range, often contain major proportions of aromatic hydrocarbons that are mainly alkylnaphtha-lenes. Also present in significant quantities are the mono-cyclic aromatic hydrocarbons such as the alkyl benzenes and certain tricyclic aromatic hydrocarbons. Isolating these hydrocarbons from each other and from the non-aromatic hydrocarbons is a difiicult and complicated process. In the past the separation, if any, was performed through selective solvent extraction.

It is an object of the present invention to provide a novel and beneficial method of separating naphthalenic compounds'f'rom petroleum. Another object is to separate aromatic compounds from non-aromatic compounds. Still another object is to separate naphthalenic compounds from cracked petroleum fractions. A specific object is to separate alkylnaphthalenes from cracked gas oil containing alkylnaphthalenes in admixture with other aromatic and/or non-aromatic hydrocarbons.

These and other objects of the present invention are accomplished by selectively complexing the desired aromatic compound with an alkali metal in a special solvent medium, separating the complex from the medium, and then decomposing the complex to recover the desired hydrocarbon.

The-charge stock used in the present invention can 'be any petroleum fraction containing naphthalenic compounds. Typical-1y the charge stock is a petroleum hydrocarbon fraction boiling within the range of 375 to 600 F. and containing at least a minor amount, e.g. 12% by weight, of naphthalenic compounds. Such fractions may have aromatic contents varying within the range of 25% to 97% but usually contain between 50% and 95% aromatics depending upon the particular operation in which the petroleum fractions are produced. In general, the substituted condensed ring aromatic hydrocarbons constitute about 20% to 80% of the total aromatic hydrocarbons present in the charge stock. The preferred hydrocarbon charge stocks are obtained in both catalytic and thermal cracking processes and in operations in which combinations of catalytic and thermal cracking steps are utilized. Thus,vtypically the charge stocks preferred for use in the present invent-ion are petroleum hydrocarbons, such as cracked gas-oils, boiling between 375 and 600 F., having a gravity between 5 and 45 API, a sulfur content from negligible to 3% by weight or more, and containing at least a minor amount of naphthalenic compounds.

According to the present invention, a charge stock of the type described hereinabove is contacted with an alkali metal, preferably in finely dispersed form. It was discovered that the alkali metal selectively reacted with the naphthalenic compounds forming a complex of alkali metal naphthalene compounds. Suitable examples of the alkali metal that may be used include sodium, potassium and lithium. Sodium is preferred since it has shown excellent selectivity for only naphthalenic-compounds, is cheaper and usually more readily available. Use of chemically pure sodium is not essential, however, as mixtures containing a substantial amountof sodium can be used as well as alloys of sodium. and potassium, and of sodium and lithium.

The metallation reaction between the sodium and the naphthalenic compounds contained in the charge stock is carried out in a reaction medium consisting of a selected ether of a particular class of ethers that appear to possess the property. of promoting or aiding in the formation of the sodium-hydrocarbon complex. The ether can be any aliphatic monoether having a methyl group. Examples include dimethyl ether, methyl ethyl ether, methyln-propyl ether, methyl isopropyl ether, and mixtures of these methyl ethers. Other satisfactory ethers include certain polyethers such as the acyclic and cyclic polyethers which are derived by replacing all of the hydroxyl hydrogen atoms of the appropriate polyhydric alcohol by .alkyl groups. Typical examples are the-ethylene glycol dialkyl ethers such as the dimethyl, methyl ethyl, diethyl, methyl butyl, ethyl butyl, dibutyl, and butyl lauryl ethylene glycol ethers, trimethylene glycol dirnethyl ether, glycerol trimethyl ether, glyceroldimethyl ethyl ether, and diethylene glycol methyl ethyl ether, glycol formal, methyl glyceral formal, and the like. The methyl monoethers are preferred. Either dimethoxy ethane or dimethyl ether is distinctly preferred.

The ethers used in conjunction with the metallation reaction should not contain any groups such as hydroxyl or carboxyl which are distinctly reactive toward the alkali metal. Although the ether may react in some manner not completely understood, it must not be subject to any action that destroys the ether or uses up the alkali metal or tends to induce polymerization rather than the desired reaction.

Inert media may be present in the reaction medium in limited amounts without affecting the metallation reaction. Usually the inert media is introduced with the alkali metal dispersion as the suspending liquid for the metal. Care should "be taken in adding inerts. As the active ether is diluted by the increased addition of inerts, a minimum concentration of ether is required below which the promoting effect of the ether is not evident. The exact minimum concentration of ether depends upon the particular charge stock and particular ether being used and upon the reaction conditions employed. In any event the concentration of ether in the reaction mixture should at all times be maintained at a sufiicient level to have a substantial effect upon the desired metallation reaction. Typically, at least 50% by weight of active ether in the reaction medium should be employed.

The alkali metal dispersion is prepared by using one or more dispersing agents capable of promoting rapid and complete breakdown of the discrete alkali metal particles. These dispersing aids include copper oleate, aluminum stearate, oleic acid, aluminum octanoate, calcium stearate, aluminum laurate, lead naphthenate, zinc stearate, and other metallic soaps. Lecithin, polymers, rubber, etc. can also be used in some cases.

The reaction temperature for the metallation reaction is preferably held below 0 C., with the temperature range between 20 C. and ferred.

-50 C. being particularly pre In one embodiment of the present invention, an alkali metal dispersion is prepared by placing an inert hydrocarbon in a suitable vessel with the appropriate amount of alkali metal. The mixture is heated until the alkali metal is in a molten state. Then a dispersing aid such as the dimer of oleic acid is added using severe agitation. After the addition of the dispersing aid has been completed all agitation is stopped and the dispersion is allowed to cool to room temperature.

The dispersion, preferably suspendedin an inert liquid such as saturated dibutyl ether, normal octane, n-heptane, and the like; is then added to the special ether which has been precooled to and preferably maintained between 20 to -50 C. The charge "stock is next added slowly and in small increments. One quite satisfactory method is to introduce the charge material at approximately the same rate at which it complexes with the alkali metal. Preferably, constant agitation is used during this addition of charge stock.

The reaction mixture comprising the alkali metal naphthalenic complex, i.e. sodio-naphthalenic; uncomplexed hydrocarbons, unreacted alkali metal and special ether are next washed with a light hydrocarbon having from 4 to carbon atoms per molecule, such as n-pentane, in order to precipitate the complex out of the reaction mixture. The precipitated complex and unreacted alkali metal are separated from the mixture by, say, filtration. The filtrate, which comprises, say, gas oil less the complexed aromatics are recovered in subsequent operations.

The complex and unreacted alkali metal mixture is then subjected to conditions which decompose the complex into naphthalenic compounds, alkali metal, and liberated special ether. The alkali metal is recovered, say, by filtration and, preferably, is reused in the process. The ether and naphthalenic compounds are also separated, for example, by distillation, and the ether, preferably, reused. Naphthalenic compounds of high purity and yield are recovered.

The complex can be decomposed by any means known to the art. .Usually, however, decomposition can be effected by the simple expedient of warming the complex to room temperature, e.g. 50 C., while subjecting the complex to reduced pressures of, say, 100-200 mm. Hg absolute. On the other hand, the complex can be decomposed by washing it with a large amount of light hydrocarbon. For example, if n-heptane is used as a wash liquid, the following results might be expected from varying the ratio of wash liquid to complex:

1:1=complex will not precipitate 1: 1=complex will decompose lzl=complex precipitates readily The exact ratio to use will be apparent to those skilled in the art from a knowledge of the reaction conditions and the characteristics of the reactants used. Preferably, the complex is decomposed by the application of heat.

The following example illustrates one specific embodiment of the present invention:

EXAMPLE 100 milliliters of dimethyl ether was mixed with 4.6 grams of finely dispersed sodium metal. The mixture was heated to 110 C. with constant stirring for approximately 10 minutes and then cooled to 50 C. afterv The diluted 9 milliliters of naphthalene and higher aromatic hydrocarbons were recovered. The loss of sodium metal was less than 5% by Weight. The dicyclic aromatic hydrocarbon recovery was better than 70% by volume of those present in the charge gas oil.

Equivalent modifications to this invention will become readily apparent to those skilled in the art.

I claim:

1. Method of separating naphthalenic compounds from a petroleum fraction boiling within the range of 375 to 600 F. and containing naphthalenic compounds which comprises the steps of:

(a) admixing said petroleum fraction with a finely dispersed alkali metal at a temperature below 0 centigrade,

(i) in the presence of a selected ether to form alkali metal naphthalene compounds,

(b) separating the said alkali metal naphthalene compounds from the residual petroleum fraction,

(c) decomposing said alkali metal naphthalene compounds by heating same to form naphthalene compounds, and,

(d)) recovering the naphthalenic compounds formed. 7

2. Method according to claim 1 wherein said alkali metal is sodium.

3. Method of separating alkylnaphthalenes from a petroleum fraction boiling within the range of 375 to 600 F. and containing alkylnaphthalenes which comfrom a petroleum hydrocarbon fraction boiling within the range 375 to 600 F. and containing at least a minor amount of naphthalenic compounds which comprises the steps of: I

(a) subjecting said petroleum fraction to reaction in a reaction Zone with finely dispersed sodium metal at a temperature below 0 centigrade,

(i) in the presence of a special ether selected from the group consisting of aliphatic monoethers having a methyl group, polyethersderived from an aliphatic polyhydric alcohol having all of the hydroxyl hydrogen atoms replaced by alkyl groups, and mixtures thereof,

(ii) thereby forming a reaction mixture comprisprising a sodio-naphthalenic complex, uncom plexed hydrocarbons, and said special ether;

(b) diluting said reaction mixture with an inert hydrocarbon diluent having 4 to 10 carbon atoms per molecule thereby precipitating said complex from said reaction mixture,

(c) separating said precipitated complex from the diluted reaction mixture,

(d) decomposing'said complex, and

(e) recovering naphthalenic compounds as a product of decomposition.

6. Method according to claim 5 wherein said petroleum hydrocarbon fraction is selected from the group consisting of cracked gas oil and aromatic fractions separated;

8. Method according to claim 7 wherein said ether is 1,2-dimethoxyethane and said diluent is n-pentane.

9. Method according to claim 2 wherein said admixing is performed at a temperature between 20 C. and -50 C.

10. Method according to claim 4 wherein said reaction takes place at a temperature between 20 C. and 50 C.

11. Method according to claim 5 wherein said reaction takes place at a temperature between -20 C. and 50 C.

12. Method according to claim 8 wherein said reaction takes place at a temperature between 20 C. and --50 C.

References Cited by the Examiner UNITED STATES PATENTS Scott 260-665 Scott 260-665 Scott 260-665 Scott 260-665 Vanderbilt 208-294 Frank et al. 260-665 J00 et al. 208-294 DELBERT E. GANTZ, Primary Examiner. ALPHONSO D. SULLIVAN, Examiner.

C. E. SPRESSER, Assistant Examiner. 

1. METHOD OF SEPARATING NAPHTHALENIC COMPOUNDS FROM A PETROLEUM FRACTION BOILING WITHIN THE RANGE OF 375* FROM 600*F. AND CONTAINING NAPHTHALENIC COMPOUNDS WHICH COMPRISES THE STEPS OF: (A) ADMIXING SAID PETROLEUM FRACTION WITH A FINELY DISPERSED ALKALI METAL AT A TEMPERATURE BELOW 0* CENTIGRADE, (I) IN THE PRESENCE OF A SELECTED ETHER TO FORM ALKALI METAL NAPHTHALENE COMPOUNDS, (B) SEPARATING THE SAID ALKALI METAL NAPHTHALENE COMPOUNDS FROM THE RESIDUAL PETROLEUM FRACTION, (C) DECOMPOSING SAID ALKALI METAL NAPHTHALENE COMPOUND BY HEATING SAME TO FORM NAPHTHALENE COMPOUNDS AND, (D) RECOVERING THE NAPHTHALENIC COMPOUNDS SO FORMED. 